Like the topic says I need a script that can check if a file has been selected, and then activate the submitbuttom, I've tried some codes that I found on google, but without success.

So now I ask you guys for help!

This is my form:
<form name='newad' method='post' enctype='multipart/form-data'  action=''>
<input NAME='image' TYPE='file' size='50'><INPUT TYPE='submit' VALUE='Upload' name='submit' OnClick="na_change_img_src('load', 'document', 'load.gif', true);"load', 'document', 'load.gif', true);'>